Stock cartouche highlighting?

I sold an old G-43 several years ago. I didn't keep it primarily because the metal had been reblued and the stock heavily sanded...to the point where the stock cartouche was barely visible.

I ran into the guy I sold it to at a recent gunshow...complete with my old G-43. He had done a good job of highlighting the metal stamps and numbers in white, something which I have always found attractive. What wowed me was the job he did in blackening in the stock cartouche...it looked really great.

Any ideas as to how he did this?

Rubbing some pure tung oil into my Garand stock really brought out the cartouche.

It didn't make it black, but made it pop nicely with a similar tone to the walnut, but darker.

Not sure if tung oil is an accurate finish for a G-43, though.